Previously, we demonstrated that insulin inhibits lipolysis in fat cells by both cAMP-related and cAMP-independent processes, and the data indicated that the latter effect was due to insulin activation of a phosphatase that dephosphorylated and, thus, inactiviated the hormone-sensitive lipase. To test this hypothesis we have purified a cholesterol esterase from bovine adrenal that is identical to the adipocyte lipase for use as a tool in studying the phosphorylation state of lipase in fat cell extracts. We also showed previously, in lipolysis studies, that the adenylate cyclase-linked receptors in fat cells are linked also to cAMP-independent processes. This conclusion was confirmed by glucose transport studies in which we established that these receptors regulate, in a cAMP-independent manner, both sensitivity to insulin for initiating the glucose transport response and the intrinsic activity of the glucose transporter without effecting a change in transporter location. These findings indicate that receptors, such as those for Beta-adrenergic agents and adenosine, play a far greater role in adipocyte metabolism than adenylate cyclase regulation. Further evidence for functional interactions among receptor mechanisms is provided by our finding that adenylate cyclase activity in purified adipocyte membranes is stimulated by the purified calcium/phospholipid-dependent, enzyme, protein kinase C. The kinase effect on cyclase is calcium-dependent, enhanced by phorbol esters, and inhibited by known inhibitors of the kinase. Such data suggest that one hormone, by binding to its receptor and activating phospholipid turnover, resulting in formation of diacylglycerol, a protein kinase C activator, might indirectly modify actions of other hormones that act directly on adenylate cyclase.